1. Field of the Invention
The present invention relates to a noise suppressor for reducing propagation of a floor impact noise and other types of noise generated in an upper story to a lower story in a two- or more-storied building.
2. Description of the Prior Art
There have been proposed various types of methods as a soundproof means against floor impact noises. For instance, in published Japanese Utility Model Application, KOKAI (Early Publication) No. (hereinafter referred to briefly as xe2x80x9cJU-A-xe2x80x9d) 3-89834, it is taught that arrangement of sound insulating materials each having angular projections formed on the bottom surface thereof on the floor panels makes smaller transmission of vibration to a floor surface and, as a result, a function of noise suppression is enhanced. Also, in JU-A-61-87815 it is taught that the noise suppression effect can be achieved by forming a floor panel body with a foaming material and also forming concave grooves in the rear surface thereof. Furthermore, a floor framing method in which the noise suppression effect can be achieved by incorporating wooden floor joists into the dry-floor construction method is disclosed in JU-A-62-203332.
By the way, apart from the passive noise control obtained by improving material or construction as described above, an active noise control for xe2x80x9celiminating a sound with another type of soundxe2x80x9d has been examined and utilized in various fields. For instance, a device which directionally generates an additional sound in a working area against a noise propagated from a noise area on the same floor to locally suppress the noise is disclosed in published Japanese Patent Application, KOKAI No. (hereinafter referred to briefly as xe2x80x9cJP-A-xe2x80x9d) 5-108083. Also, a soundproof device for suppressing mechanical noises made outside a soundproof box with sound waves in the soundproof box installed in a site of a manufacturing line in a factory is disclosed in JP-A-6-240776. In addition to the disclosures described above, JU-A-4-133298 discloses an active system of a noise suppressor for suppressing noises propagating through a duct to rooms also with sound waves in a multiple dwelling house or the like.
These active types of noise control are effective in suppressing noises by basically making use of interference between sound waves therewith although the control systems are more or less different from each other. Namely, the control system described above is based on the principle in which a noise is counteracted by adding a sound wave having a reverse phase and also having the same sound pressure thereto to cause interference between the sound waves to eliminate the noise.
The problem concerning floor impact noises has been increasing in recent years in association with increase of multiple dwelling houses as well as with higher density of environments for living, and especially in constructions based on wooden materials, it has been difficult to take effective countermeasures for reduction of the floor impact noises because there are more components as compared to concrete constructions, or because the construction itself is complicated. In a case where the technology of passive noise control based on improvement of the floor materials or the construction described above is employed, floor impact noises are somewhat reduced, but a sufficient noise suppression effect can not eventually be obtained thereby, and further, there may occur a problem other than those relating to noises that the strength of the floor itself is reduced. Furthermore, an application of the technology of the passive noise control to existing buildings requires an extensive scale of construction works, which is practically difficult to be realized.
There is not any known case in which the technology of active noise control using the interference between sounds has actually been applied to eliminate floor impact noises.
It is, therefore, an object of the present invention to provide a floor impact noise suppressor which enables floor impact noises and other types of noise (hereinafter referred to collectively as xe2x80x9cfloor impact noisesxe2x80x9d) to be reduced by applying the technology of active noise control to a two- or more-storied building without changing floor materials or construction and without reducing the strength of the floor itself more effectively as compared to the technology of passive noise control based on the conventional technology.
In accordance with the present invention, to achieve the object described above, there is provided a floor impact noise suppressor for reducing propagation of floor impact noises generated in an upper story to a lower story in a multi-storied building, which comprises a reference sensor for detecting a floor impact noise generated in the upper story and converting it to an electric signal; a sound wave generating means for emitting a sound wave for suppressing the floor impact noise; an error sensor for detecting an interference sound caused by interference between the floor impact noise and the sound wave emitted from the sound wave generating means and converting it to an electric signal; and a controlling means for computing, according to an adaptive control based on the electric signals from the reference sensor and the error sensor, a driving signal for emitting a sound wave adapted to eliminate the floor impact noise by means of negative phase interference from the sound wave generating means, the reference sensor being disposed in the periphery of the floor of the upper story or in any place from the bottom of the floor of the upper story to the bottom surface of the ceiling of the lower story, the sound wave generating means being disposed at a position lower than that of the reference sensor, and the error sensor being disposed inside a room in the lower story.
In a preferred embodiment, it is desirable to use at least two error sensors to more effectively suppress noises by scanning the error sensors one by one and successively updating an impulse response to an adaptive filter, and also it is desirable to use at least two units of sound wave generating means to generate without fail sound waves for eliminating floor impact noises, the sound waves each having a phase reverse to that of the noise to be eliminated. Furthermore, in a multi-storied building, in a case of a heavy weight floor impact noise as defined in JIS (Japanese Industrial Standard) A-1418, generally, the lower the frequency is, the higher a level of the floor impact noise is, and in a case of a light weight floor impact noise, although the level is different according to a floor construction, a peak of the level of the floor impact noise is generally in a range from 25 to 125 Hz (50 to 250 Hz in a model on the scale of one to two (1/2)) in an actual building. It is therefore desirable to set a signal received by the controlling means at a frequency not higher than 200 Hz, preferably not more than 150 Hz in order to effectively suppress a floor impact noise in the low frequency band.